1. Field of the Invention
The present invention relates to an electromotive actuator for use in operating, for example, a movable nozzle of a rocket and to a method for controlling the same.
2. Description of Related Art
Conventionally, as such an electromotive actuator as mentioned above, there is, for example, an electromotive actuator 51 which, as shown in FIG. 6, includes: a first motor 55 and a second motor 56 accommodated in a parallel state to each other in a housing 54 which is pivotally connected to a fuselage R1; a ball screw 50 disposed in parallel to the first motor 55 and the second motor 56; a third gear 58 attached to a lead 52 of this ball screw 50 and simultaneously engaged both with a first gear 57 and a second gear 59 which are attached to respective output shafts of the first motor 55 and the second motor 56; and an arm 61 attached coaxially with the lead 52 to a housing 60 which is integrally structured with a nut 53 of the ball screw 50.
This electromotive actuator 51 is so structured that, for example, when the first motor 55 is malfunction, the lead 52 of the ball screw 50 is driven only with the second motor 56 to move the arm 61 together with the housing 60 in an arrow X direction.
As another electromotive actuator different from this electromotive actuator 51, there is an electromotive actuator 71 which, as shown in FIG. 7, includes: a first motor 75 and a second motor 76 accommodated in a coaxial state with each other in a housing 74 which is pivotally connected to a fuselage R2; a ball screw 70 disposed perpendicularly to the first motor 75 and the second motor 76; a differential gear array 79 which connects respective output shafts of the first motor 75 and the second motor 76 to a lead 72 of this ball screw 70; and an arm 81 attached coaxially with the lead 72 to a housing 80 which is integrally structured with a nut 73 of the ball screw 70, and in the first motor 75 and the second motor 76, a first brake 77 and a second brake 78 for restricting the rotations of the respective output shafts are provided.
This electromotive actuator 71 is so structured that, for example, when the first motor 75 is malfunction, the first brake 77 brakes the output shaft of the first motor 75 and the lead 72 of the ball screw 70 is driven only with the second motor 76 to move the arm 81 together with the housing 80 in an arrow X direction.
Furthermore, as another electromotive actuator different from the electromotive actuators 51, 71 described above, there is an electromotive actuator 91 which, as shown in FIG. 8, includes: a motor 95 accommodated in a housing 94 which is pivotally connected to a fuselage R3; a lead 96 of a ball screw disposed coaxially with this motor 95; a nut 98 of the ball screw integrally structured with a housing 97 which is coaxially disposed with the motor 95; and an arm 99 which is positioned on a side of the housing 97 opposite the nut 98 and which is coaxial with the motor 95, and this electromotive actuator 91 is so structured that the arm 99 is moved in an arrow X direction together with the housing 97 by rotating the motor 95.
In this case, as a multiphase motor used in the above-described electromotive actuators 51, 71, 91, there is, for example, a three-phase brushless motor 100 which is, as shown in FIG. 10, provided with totally two sets of windings 101, 102 of an A system and a B system. The windings 101, 102 of this three-phase brushless motor 100 are both connected to inverters C, C respectively and electric currents flowing through the two sets of the windings 101, 102 are feedback to interface circuits 105, 106 via these inverters C, C respectively to perform electric current control.
In the above-described electromotive actuators, however, the electromotive actuator 51 shown in FIG. 6 has a problem that efficiency of the electromotive actuator 51 is lowered due to an inertia load of the first motor 55 when the first motor 55 is malfunction and only the second motor 56 is operated.
Moreover, in order to prevent the influence of the inertia load of the first motor 55, a clutch mechanism becomes necessary, and there exists a problem that reliability of a power transmission system of the electromotive actuator 51 is lowered.
The electromotive actuator 71 shown in FIG. 7 has a problem that, since its mechanism system is relatively complicated, reliability cannot be said to be high, and in addition, manufacturing cost may possibly be increased.
Furthermore, in the electromotive actuator 91 shown in FIG. 8, when the arm 99 is fixed in a predetermined position while the motor 95 is burdened with a load, the position is maintained by a positioning servo based on a feedback signal from a not-shown position sensor, so that electric currents are concentrated to a power transistor for fixing (for example, a transistor C1) of an inverter C, as shown in FIG. 9, to increase heat generation due to a resistance loss of this power transistor C1, and therefore, there exists a problem that it cannot be said that there is no possibility that the inverter C is damaged.
Meanwhile, in the conventional three-phase brushless motor 100 used in the above-described electromotive actuators 51, 71, 91, when, for example, the set of the windings 101 or the inverter C of the A system has a trouble, the three-phase brushless motor 100 operates only with the remaining set of the windings 102 of the B system since the two sets of the windings 101, 102 are independent from each other, but there exists a problem that its output power is reduced by half.
Moreover, there exists problems that, when even one phase out of three phases becomes out of order in the remaining set of the windings 102 of the B system, an inoperable state is caused, and in addition, the damage of one phase induces the damage of the other phases when the inverters C, C are out of order in a normal short-circuit mode. Therefore, solving these problems has been a conventional object.
The present invention is made in view of the above-described conventional problems, and an object of an invention according to claim 1 and claim 2 is to provide an electromotive actuator which can realize structure simplification and reduction in manufacturing cost without lowering power transmission efficiency and reliability; an object of an invention according to claim 3 and claim 4 is to provide an electromotive actuator and a method for controlling the electromotive actuator which can reduce a resistance loss of a power transistor, and in addition, can realize uniform thermal distribution, and as a result, can downsize an inverter and enhance reliability; and an object of an invention according to claim 5 and claim 6 is to provide a multiphase motor and a method for controlling the same which can not only prevent an inoperable state but also suppress decrease in output power even when an inverter is malfunction or one phase out of multi-phases of windings has a trouble, and in addition, which can almost eliminate the possibility that the damage of one phase induces the damage of the other phases when the inverter is out of order in a normal short-circuit mode.
An electromotive actuator according to claim 1 of the present invention comprises a first motor and a second motor, and is characterized in the structure that a lead of a ball screw is disposed coaxially with a motor rotary shaft on a side of one motor out of the first motor and the second motor and a nut of the ball screw is disposed coaxially with the motor rotary shaft on a side of the other motor out of the first motor and the second motor, thereby connecting the first motor and the second motor to each other via the ball screw. This structure of the electromotive actuator is adopted as means for solving the conventional problems described above.
An electromotive actuator according to claim 2 of the present invention is so structured that a lead brake for restricting the rotation of the lead of the ball screw is disposed on the side of one motor out of the first motor and the second motor and a nut brake for restricting the rotation of the nut of the ball screw is disposed on the side of the other motor out of the first motor and the second motor.
An electromotive actuator according to claim 3 of the present invention comprises a first motor, a second motor, and an operating section, and is characterized in the structure that a speed adding/outputting mechanism, which is connected to both of respective rotary shafts of both of the motors, for outputting a speed difference between both of the motors to the operating section is disposed between the first motor and the second motor, and that the speed difference between both of the motors is eliminated by constantly rotating both of the first motor and the second motor in the same phase to enable a fixed state of the operating section to be maintained. This structure of the electromotive actuator is adopted as means for solving the conventional problems described above.
A method for controlling an electromotive actuator according to claim 4 of the present invention is characterized in the structure that, in the electromotive actuator according to claim 3, the fixed state of the operating section is maintained by constantly rotating both of the first motor and the second motor in the same phase to eliminate the speed difference between both of the motors. This structure of the method for controlling the electromotive actuator is adopted as means for solving the conventional problems described above.
An invention according to claim 5 of the present invention is a multiphase motor which is a motor used in the electromotive actuators according to claim 1 to claim 3, comprising two sets of windings connected to inverters respectively, and it is characterized in the structure that, in the multiphase motor performing electric current control by feeding back electric currents flowing through the two sets of the windings respectively, a neutral line connected both to a neutral point of a star connection in one of the sets of the windings and a neutral point of a star connection in the other one of the sets of the windings is provided. This structure of the multiphase motor is adopted as means for solving the conventional problems described above.
A method for controlling a multiphase motor according to claim 6 of the present invention is characterized in the structure that, in the multiphase motor according to claim 5, when a failure occurs in one of phases of one of the two sets of the windings, electric current control is performed in such a manner that a substantially doubled electric current is made to flow through a phase of the other one of the sets of the windings, which is a counterpart of the phase in which this failure occurs. This structure of the method for controlling the multiphase motor is adopted as means for solving the conventional problems described above.
Since the electromotive actuator according to claim 1 of the present invention has the above-described structure, the movement of the ball screw corresponds to the sum of a rotation angle of the first motor and a rotation angle of the second motor and the redundancy of the speed sum is structured so that, for example, even when the operation of the first motor is stopped, an inertia load of this first motor does not become a load on the second motor, and thereby, degradation in power transmission efficiency is avoided.
In the electromotive actuator according to claim 2 of the present invention, when, for example, the first motor stops due to its failure, by braking the motor rotary shaft of this first motor, a drive operation can be performed only with the second motor without being influenced by the inertia load of the first motor which has stopped, though the speed is reduced by half.
Since the electromotive actuator according to claim 3 of the present invention has the above-described structure, when the fixed state of the operating section is maintained, a resistance loss of one power transistor becomes one third of that in a prior art by rotating the first motor and the second motor in the same phase so that heat generation due to the resistance loss of the power transistor is suppressed to be small.
Since the method for controlling the electromotive actuator according to claim 4 of the present invention has the above-described structure, the resistance loss of the power transistor in maintaining the fixed state of the operating section is suppressed to one third of that in a prior art, and as a result, downsizing and reliability enhancement of an inverter are realized.
The multiphase motor according to claim 5 of the present invention has the above-described structure, and therefore, in a case when the multiphase motor is, for example, a three-phase motor, when a failure in a short-circuit mode occurs in an inverter of a U-phase of one of the sets of the windings, a short-circuit electric current flows through the neutral line and does not flow to other elements, and the electric current control using the neutral line is performed in the remaining set of the windings. Consequently, almost no influence of the damage of the U-phase of one of the sets of the windings is given to the other phases, and in this case, control for automatically compensating for the electric current loss in the U-phase can be performed so that a great decrease in output power can also be suppressed.
In the method for controlling the multiphase motor according to claim 6 of the present invention, in a case when the multiphase motor is, for example, a three-phase motor, even when the inverter of the U-phase in one of the sets of the windings has a failure, a substantially doubled electric current is caused to flow through a Uxe2x80x2-phase of the other one of the sets of the windings, which is a counterpart of this U-phase, thereby controlling to have the Uxe2x80x2-phase automatically compensate for the loss in the U-phase so that the decrease in output power is suppressed to be small.